Sucrose-templated mesoporous β-Ga2O3 as a novel efficient catalyst for dehydrogenation of propane in the presence of CO 2

Article abstract of DOI:10.1016/j.catcom.2012.11.004

A series of mesoporous β-Ga₂O₃ with high surface area have been prepared using eco-friendly sucrose as a non-surfactant template and studied in relation to their performance in the dehydrogenation of propane to propylene in the presence of CO₂. Among the four sucrose-derived samples tested, the material prepared from a sucrose/Ga₂O₃ molar ratio of 4 achieved the highest propane conversion, which was approximately the double efficiency of the conventional β-Ga ₂O₃. The enhanced activity of the sucrose-derived materials is attributed to a high abundance of coordinative unsaturated surface Ga sites as a consequence of their favorable textural properties and enhanced surface areas.

Full text of DOI:10.1016/j.catcom.2012.11.004

Catalysis Communications 30 (2013) 61–65
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Sucrose-templated mesoporous β-Ga O as a novel efficient catalyst for
2
3
dehydrogenation of propane in the presence of CO2
a
a,b
a,
a,
a
a
Jia-Ling Wu , Miao Chen , Yong-Mei Liu ⁎, Yong Cao ⁎, He-Yong He , Kang-Nian Fan
a
Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, PR China
Zhejiang Chemical Industry Research Institute, Hangzhou 310023, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of mesoporous β-Ga O3 with high surface area have been prepared using eco-friendly sucrose as a
2
Received 3 September 2012
Received in revised form 31 October 2012
Accepted 2 November 2012
Available online 9 November 2012
non-surfactant template and studied in relation to their performance in the dehydrogenation of propane to
propylene in the presence of CO
from a sucrose/Ga molar ratio of 4 achieved the highest propane conversion, which was approximately
the double efficiency of the conventional β-Ga . The enhanced activity of the sucrose-derived materials
2
. Among the four sucrose-derived samples tested, the material prepared
2 3
O
2 3
O
is attributed to a high abundance of coordinative unsaturated surface Ga sites as a consequence of their favor-
able textural properties and enhanced surface areas.
Keywords:
Propane dehydrogenation
Propylene
© 2012 Elsevier B.V. All rights reserved.
Sucrose
Mesoporous β-Ga O
2 3
Carbon dioxide
1
. Introduction
Direct conversion of light alkanes to value-added olefins by on-
Ga
ever, only very few studies on the synthesis of Ga
face area. In a recent study by West et al. [13], mesoporous Ga
2
O
3
can lead to an improvement in the PDH activity. There were how-
with enhanced sur-
with a
surface area up to 307 m2
g has been synthesized via a nanocasting
2 3
O
2 3
O
−1
purpose olefin technologies may become a potentially economically via-
ble route in the coming years [1]. In this connection, much recent atten-
technique using mesoporous carbon (CMK) as a hard template. The prob-
lems inherent in this procedure are that it is extremely tedious and
time-consuming. A urea-based hydrothermal method using polyethylene
glycol (PEG) as the soft template agent has been employed for prepara-
tion has been directed to the CO
PDH), which is a potentially attractive alternative approach to produce
propylene, an important monomeric feedstock in the chemical industry
2,3]. In this valuable transformation, cheap and abundant CO serves
2
-mediated propane dehydrogenation
(
[
2
tion of a series of mesoporous β-Ga
only afford a very limited accessible surface area of ca. 29 m
2 3
O nonorods, which however can
2
−1
two distinct functions: as a mild oxidant to shift the equilibrium towards
the products and the suppression of coke deposition [4,5]. Whereas a
number of catalysts have been developed for such purpose, a persistent
challenge is the control of reaction kinetics to avoid rapid deactivation
owing to coke formation [6]. Thus far, gallium oxides have been recog-
nized as one kind of the most promising materials due to their excellent
catalytic efficiency as compared to conventional Cr- or V-based systems
g
[14].
Alternatively, sucrose is a kind of water soluble carbon source, which
has been widely employed as a simple and convenient carbon template
precursor in synthesis of high surface area α-Al
[17]. Herein, we demonstrate for the first time that, high surface area
mesoporous β-Ga materials prepared using eco-friendly sucrose as a
non-surfactant template show a significantly improved performance for
catalyzing propane dehydrogenation in the presence of CO
2 3 2
O [15,16] and ZrO
2 3
O
2 3
[7,8]. The superior performance of the Ga O -based system for PDH has
2
.
been attributed to the unique structural characteristics of coordinatively
unsaturated surface (cus) Ga3 sites [9], which is believed to be crucial
+
2. Experimental
2
for hydrocarbon activation in CO atmosphere [10]. However, the devel-
opment of new improved catalytic system exhibiting desirable stability
and activity continues to be a major challenge.
2.1. Catalyst preparation
Over the years, a number of studies have established that the popula-
tion of the catalytically relevant (cus) Ga species is a strong function of the
An appropriate amount of sucrose was dissolved in 0.25 M aqueous
Ga(NO solution at 303 K under continuous stirring. The pH of the so-
3 3
)
surface area of Ga
2
O
3
among different Ga
2
O
3
polymorphs [10–12]. In this
lution was adjusted to ca. 5 by dropwise adding of 3 M ammonia solu-
tion. After aging at 353 K for 2 h, the resulting material was oven dried
at 383 K for 24 h. The thus-obtained black precursor (2 g) was then
sense, one may rationalize that simply increasing the surface area of
transferred into a tube furnace and was initially annealed under N
(30 mL min ) at 923 K for 30 min, followed by calcination at 923 K
2
⁎
Corresponding authors. Tel.: +86 21 55665287; fax: +86 21 65643774.
E-mail addresses: ymliu@fudan.edu.cn (Y.-M. Liu), yongcao@fudan.edu.cn (Y. Cao).
−
1
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2012.11.004

62
J.-L. Wu et al. / Catalysis Communications 30 (2013) 61–65
Table 1
Summary of texture properties and NH
3
-TPD measurements.
Catalyst
S
BET (m2 g−1 (cm3 g−1
)
V
p
)
Desorption peak NH
temperature (K) (mmol gcat
3
desorbed
−
1
)
β-Ga
β-Ga
β-Ga
β-Ga
β-Ga
β-Ga
β-Ga
2
O
2
O
2
O
2
O
2
O
2
O
2
O
3
3
3
3
3
3
3
38
35
65
89
98
0.08
0.07
0.10
0.13
0.17
0.15
0.17
563
565
565
566
570
569
571
0.46
0.16
0.87
1.03
1.44
0.93
1.27
-Da
-S1
-S2
-S4
a
-S4-D 92
-S8 95
a
2 3 2 3 2 3 2 3
β-Ga O -D and β-Ga O -S4-D stand for β-Ga O and β-Ga O -S4 after reaction for
8
h on stream respectively.
by mass spectroscopy (Balzers OmniStar QMS 200). The morphology
and microstructure were analyzed by scanning electron microscopy
(SEM, Philips XL 30) and transmission electron microscopy (TEM,
JEOL-2011, operated at 200 kV).
(
)
2.3. Activity measurement
Fig. 1. XRD profiles of various β-Ga
2
O
3
samples.
Catalytic tests were performed in a fixed-bed flow microreactor at
atmospheric pressure, and the catalyst load was 200 mg. Prior to the re-
under flowing air (10 mL min−1) for 4 h. Four sucrose-templated sam-
ples with sucrose/Ga molar ratio at 1, 2, 4, and 8 were synthesized,
denoted as β-Ga -S1, β-Ga
spectively. For comparison purpose, a conventional β-Ga
action, the catalysts were pretreated at 773 K for 1 h in N
flow. The feed
containing 2.5 vol.% propane,
2
. The hydrocarbon reaction products
2
−
1
O
2 3
was at a total flow rate of 10 mL min
5 vol.% CO , and a balance of N
O
2 3
2 3
O
-S2, β-Ga
2
O
3
-S4, and β-Ga
2
O
3
-S8, re-
sample
2
2
O
3
were analyzed using an on-line gas chromatograph (Type GC-122,
Shanghai) equipped with a 6-m packed column of Porapak Q and a
flame ionization detector (FID). The permanent gaseous products, in-
was prepared by calcination of gallium nitrate at 923 K for 4 h [18].
2
.2. Catalyst characterization
2 2
cluding N , CO, and CO , were analyzed on-line by another GC equipped
with a TDX-01 column and a thermal conductivity detector (TCD).
The BET specific surface areas of the samples were determined by
adsorption–desorption of nitrogen at 77 K using a Micromeritics TriStar
000 equipment. The X-ray powder diffraction (XRD) measurements of
3. Results and discussion
3
the catalysts were carried out on a Germany Bruker D8Advance X-ray dif-
fractometer using nickel filtered Cu Kα radiation at 40 kV and 20 mA.
The acidic property of each catalyst was characterized by ammonia
It is known that gallium oxide has five different polymorphs (α-, β-,
γ-, δ-, and ε-Ga
any other form of Ga
above 1173 K [19]. The diffraction profiles for the sucrose-derived
Ga samples along with conventional β-Ga are shown in Fig. 1.
2
O
3
), among which β-Ga
2 3
O can be obtained by heating
2 3
O
or gallium hydrates in air with temperature
temperature-programmed desorption (NH
3
-TPD). NH
3
was adsorbed at
3
93 K after pre-treatment at 773 K in an He stream. The desorbed NH
3
2
O
3
2 3
O
in flowing He gas was quantified (NH
2
fragment of mass number 16)
The characteristic peaks of β-Ga
2
O
3
(JCPDS card: no. 41-1103) are
a
b 0.30
1
1
1
40
20
00
0
.25
0.20
8
6
4
2
0
0
0
0
0
0
0
0
.15
.10
.05
0.00
0.0
0.2
0.4
0.6
0.8
1.0
1
10
100
Relative pressure (P /P0)
Pore size (nm)
Fig. 2. Nitrogen adsorption–desorption isotherms (a) and pore size distributions (b) for Ga
▲) β-Ga -S8.
2 3 2 3 2 3 2 3 2 3
O samples: (■) β-Ga O ; (□) β-Ga O -S1; (●) β-Ga O -S2; (▽) β-Ga O -S4; and
(
2 3
O

J.-L. Wu et al. / Catalysis Communications 30 (2013) 61–65
63
a
b
c
d
e
f
g
2 3 2 3 2 3 2 3 2 3 2 3 2 3
Fig. 3. SEM images of (a) β-Ga O ; (b) β-Ga O -S1; (c) β-Ga O -S2; (d) β-Ga O -S4; and (e) β-Ga O -S8; and TEM images of (f) β-Ga O and (g) β-Ga O -S4.
observed for all samples, demonstrating that the most stable form of
Ga was achieved via the sucrose-template synthesis. The sucrose-
derived β-Ga samples show obviously lower crystallinity, as reflected
from their broadened peaks and decreased diffraction signals relative to
that for conventional β-Ga . In general, the crystallinity for the five
samples decreased in the following order: β-Ga >β-Ga -S1>
β-Ga -S2>β-Ga -S4>β-Ga -S8.
The corresponding nitrogen adsorption–desorption isotherms and
pore size distributions of the Ga samples are presented in Fig. 2. All
samples show typical type IV isotherms characteristic of mesoporous
structures, among which H3 [20] and H1 [21] hysteresis loops were re-
spectively identified for conventional β-Ga O and the sucrose-derived
2 3
samples. As summarized in Table 1, the sucrose-templating approach
can afford the production of a series of mesoporous samples with favor-
able textural properties and enhanced surface areas. The fact that the
resultant materials are pure white in color suggests a complete tem-
plate removal during the calcination step, as confirmed from the
thermogravimetry analysis (Fig S3). The SEM images of conventional
2 3
O
2
O
3
2 3
O
2
O
3
2 3
O
2
O
3
2
O
3
2 3
O
2 3
O

64
J.-L. Wu et al. / Catalysis Communications 30 (2013) 61–65
β-Ga
2
O
3
and sucrose-derived samples are shown in Fig. 3. It is observed
presents a solid bulk structure, while the
we are aware, this value compared favorably with the exceptionally
high activity obtained with the Ga -Al solid solutions [23]. It is
that conventional β-Ga
O
2 3
O
2 3
2 3
O
sucrose-templated samples display distinct sponge-like morphology, a
feature probably as a result of the carbon template removal during com-
bustion processing. Note that the sample prepared with higher sucrose/
also found that the catalytic performance show an excellent correlation
with the surface acidity data (Fig. S2). Therefore, in line with the broad
literature documenting the PDH reaction over Ga-based materials, it ap-
pears that a high abundance of surface Lewis acid Ga sites is the key fac-
Ga
veals a much smaller average particle size of β-Ga
tive to that of the conventional β-Ga (Fig. 3f), in line with the
microstructural crystallinity as reflected from the XRD measurements.
Surface acidity of these Ga samples was measured by NH -TPD
experiments. A broad asymmetric NH desorption peak is registered
O
2 3
ratio possesses higher porosity. Moreover, the TEM analysis re-
2 3
O -S4 (Fig. 3g) rela-
tor in achieving high catalytic activity of sucrose-derived Ga
2 3
O catalysts
2 3
O
[11,22].
2 3
As far as the stability is concerned, after 8 h run, conventional β-Ga O
O
2 3
3
lost 79% of its initial activity, while the sucrose-templated samples show
conversion loss corresponding to 43–56% of their initial values. This re-
veals another attractive advantage of the sucrose-templated samples for
3
in the TPD profiles for all five samples as shown in Fig. S1, consistent
with the results observed by Zheng et al. [18]. The peak temperatures
of the five samples are all located within 560–575 K, indicating the
presence of only marginal variation in the acid strength for all sam-
ples. Nonetheless, there is a significant difference in the total amounts
2 3
prolonging the lifetime of β-Ga O catalyst. However, deactivation is
still severe for the sucrose-templated samples, and regeneration therefore
seems indispensable from the perspective of application. Note that such
deactivation could be largely ascribed to the blocking of the active Lewis
acid sites by carbon deposition, rather than a significant degradation
of the surface acidity between the two types of β-Ga
cifically, the total acidity of the four sucrose-derived samples is ap-
proximately 1–2 times higher than that of the conventional β-Ga
Table 1). Previous studies on the surface property of β-Ga have
2 3
O samples. Spe-
of the textural or structural properties of the mesoporous β-Ga
material (Table 1). For regenerating β-Ga -S4 that reacted 8 h on
stream at 773 K, the reaction was interrupted under an N stream, and
2 3
O -S4
2
O
3
2 3
O
(
O
2 3
2
revealed that the Lewis acid centers comprise mainly the structurally
defective Ga sites characteristics of (cus) nature [9,22]. Thus, it fol-
lows that the remarkably increased acid sites of the sucrose-derived
samples can be largely attributed to a higher density of surface de-
fects as a consequence of the decreased crystallinity and structural
modification as inferred from XRD and TEM studies.
then air was introduced at 923 K to burn off carbon species deposited
on the catalyst (Fig. 5). After the first regeneration, the initial propane
conversion for β-Ga O -S4 amounted to 39% at 773 K, which is slightly
2 3
lower than that for the fresh sample (43.7%). However, after the second
and third regenerations, only marginal variations in initial activity were
observed. Analogous phenomenon was reported by Zheng et al. in regen-
The dehydrogenation of propane over the β-Ga
O
2 3
samples in the
2 3
eration of β-Ga O [18].
presence of CO was investigated at 773 K, and the catalytic activity
2
and product selectivity data were shown in Fig. 4. The major product
formed in the reaction is propylene, with the minor products being eth-
ane, ethylene and methane. During the 8 h run, the selectivities of pro-
pylene remain above 86% for the five catalysts (Fig. 4), among which
slightly higher values were achieved over the templated samples. It is in-
teresting to note that the sucrose-derived samples gave consistently
higher propane conversion during the reaction, showing that the textur-
4. Conclusions
The present work demonstrates the high potential of using environ-
mentally friendly sucrose as a non-surfactant template to prepare
mesoporous β-Ga
2
O
3
materials with favorable textural and structural
. It is important
properties for the dehydrogenation of propane with CO
2
al properties of the β-Ga
reaction. Worth mentioning is that over β-Ga
specific surface area, a conversion of propane (43.7%) approximately
2
O
3
materials play a significant role in the titled
to highlight here that this approach is not limited to the use of sucrose
as the carbohydrate-based carbon sources (see Table S1). The present
findings may provide new opportunities for the rational design of new
mesostructured gallium oxide catalyst systems for advanced applications.
2 3
O -S4 with the highest
twice that of conventional β-Ga
O
2 3
(23.8%) can be achieved. As far as
a
b 100
90
5
4
4
3
3
2
2
1
1
0
5
0
5
0
5
0
5
0
5
0
80
70
60
50
β-Ga O
3
40
30
20
10
0
2
β-Ga O -S1
2
3
β-Ga O -S2
2
3
β-Ga O -S4
2
3
β-Ga O -S8
2
3
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
8
Time on stream (h)
Fig. 4. Conversion of propane (a) and selectivity to propylene (b) for β-Ga
2
O
3
samples.

J.-L. Wu et al. / Catalysis Communications 30 (2013) 61–65
65
5
4
3
2
1
0
0
0
0
0
0
References
[
1] R. Grabowski, Catalysis Reviews 48 (2006) 199–268.
[
2] B.J. Xu, B. Zheng, W.M. Hua, Y.H. Yue, Z. Gao, Journal of Catalysis 239 (2006)
470–477.
[
[
[
[
3] Y. Sakurai, T. Suzaki, N. Ikenaga, T. Suzuki, Applied Catalysis A 192 (2000)
281–288.
4] Y.M. Liu, Y. Cao, K.K. Zhu, S.R. Yan, W.L. Dai, H.Y. He, K.N. Fan, Chemical Commu-
nications (2002) 2832–2833.
5] H.Y. Li, Y.H. Yue, C.K. Miao, Z.K. Xie, W.M. Hua, Z. Gao, Catalysis Communications
8
(2007) 1317–1322.
6] S.B. Wang, Z.H. Zhu, Energy and Fuels 18 (2004) 1126–1139.
[7] K. Nakagawa, M. Okamura, N. Ikenaga, T. Suzuki, T. Kobayashi, Chemical Commu-
nications (1998) 1025–1026.
[
8] K. Nakagawa, C. Kajita, K. Okumura, N.-o. Ikenaga, M. Nishitani-Gamo, T. Ando, T.
Kobayashi, T. Suzuki, Journal of Catalysis 203 (2001) 87–93.
[9] E.A. Gonzalez, P.V. Jasen, A. Juan, S.E. Collins, M.A. Baltanas, A.L. Bonivardi, Surface
Science 575 (2005) 171–180.
[
10] S.E. Collins, M.A. Baltanas, A.L. Bonivardi, The Journal of Physical Chemistry B 110
(2006) 5498–5507.
[11] S.E. Collins, M.A. Baltanas, A.L. Bonivardi, Langmuir 21 (2004) 962–970.
[12] V.B. Kazansky, I.R. Subbotina, A.A. Pronin, R. Schlogl, F.C. Jentoft, The Journal of
Physical Chemistry. B 110 (2006) 7975–7978.
0
4
8
12
16
20
24
28
32
36
Time on stream (h)
[
[
13] C. West, R. Mokaya, Chemistry of Materials 21 (2009) 4080–4086.
14] W. Zhao, Y. Yang, R. Hao, F. Liu, Y. Wang, M. Tan, J. Tang, D. Ren, D. Zhao, Journal of
Hazardous Materials 192 (2011) 1548–1554.
2 3
Fig. 5. Regeneration tests of β-Ga O -S4 catalyst.
[
15] R.N. Das, A. Bandyopadhyay, S. Bose, Journal of the American Ceramic Society 84
(
2001) 2421–2423.
Acknowledgments
[16] L.D. Mitchell, P.S. Whitfield, J. Margeson, J.J. Beaudoin, Journal of Materials Science
Letters 21 (2002) 1773–1775.
[
17] Y. Wu, A. Bandyopadhyay, S. Bose, Materials Science and Engineering A 380
2004) 349–355.
This work was financially supported by the National Natural Science
Foundation of China (21073042, 21273044), the New Century Excellent
Talents in the University of China (NCET-09-0305), the National Basic
Research Program of China (2009CB623506), and the Science & Tech-
nology Commission of Shanghai Municipality (08DZ2270500 and 12
ZR1401500).
(
[18] B. Zheng, W.M. Hua, Y.H. Yue, Z. Gao, Journal of Catalysis 232 (2005) 143–151.
[19] R. Roy, V.G. Hill, E.F. Osborn, Journal of the American Chemical Society 74 (1952)
7
19–722.
20] J. Yu, J.C. Yu, M.K.P. Leung, W. Ho, B. Cheng, X. Zhao, J. Zhao, Journal of Catalysis
17 (2003) 69–78.
[
2
[21] F.C. Gennari, A.C. Ramos, A. Condo, T. Montini, S. Bengio, A. Cortesi, J.J.A. Gamboa,
P. Fornasiero, Applied Catalysis A 398 (2011) 123–133.
[
[
22] A. Vimont, J.C. Lavalley, A. Sahibed-Dine, C.O. Arean, M.R. Delgado, M. Daturi, The
Journal of Physical Chemistry B 109 (2005) 9656–9664.
23] M. Chen, J. Xu, F.Z. Su, Y.M. Liu, Y. Cao, H.Y. He, K.N. Fan, Journal of Catalysis 256
Appendix A. Supplementary data
(2008) 293–300.
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.catcom.2012.11.004.